TABLE 3.

Virulence in mice of mrgA mutant strains as assessed by competition assays

Strain	Relevant genotype and phenotype	Geometric mean in vivo competition indexa
		Lung infection	Carriage	Bacteremia
AC1500	ΔmgrA Smr Spcr	0.26 (12)	0.034 (6)	2.1 (8)
AC1272	mgrA::magellan2 Smr Cmr	0.47 (8)	0.58 (6)	NDb
STM206	mgrA 5′-UTR::magellan2 Smr Cmr	<0.023 (4)	0.009 (6)	0.56 (3)

^aThe geometric mean of the in vivo competition index was determined. The numbers in parentheses are the numbers of animals infected in the experiments. For the experiments in which no mutant bacteria were recovered from an animal the number 1 was used as the numerator when the in vivo ratio for the animal was determined; thus, the in vivo mean competition index is less than the calculated value. The values in boldface type are significantly different (P < 0.05, as determined by the Student two-tailed t test).

^bND, not determined.